re-enable read_only_sharded suite

Because these tests restart a shard in queryableBackupMode, they must provide the shardIdentity document for the restarted shard to use through the overrideShardIdentity startup parameter.

However, this parameter must be passed through a yaml configuration file (by design).

Since the shardIdentity document must contain a valid config connection string, we need to add a workaround to either:

1) be able to know before-hand what the config connection string will be, and create a dummy yaml config file in jstests/libs, OR
2) somehow determine the config connection string at runtime and write it to a config yaml file through the javascript helpers for running bash commands (will work for linux-only)

and point the restarted shard to the yaml config file.